Method and system for communication by television



W v. K. ZWORYKIN METHOD AND SYSTEM FOR COMMUNICATION BY TELEVISION Filed Sept. 25

[M 'ENTOR. I Vladimir K. ZW org Km,

l5 ATTORNE}.

Patented Apr. 24, 1934 rm'rnon AND SYSTEM FOR CORIMUNIG A- TIDN BY TELEVISION Vladimir Kosman Zworymn,

Haddonfield, N. 3.,

assignor, by mesne assignments, to Radio Corporation of America, New York, N.- Y., a corporation of Delaware Application September 25, 1930, Serial No. 484,309

9 Claims.

My invention relates to improvements in method and system for communication by television.

In systems for television reception employing a cathode ray tube having a fluorescent screen which the stream or ray of electrons is caused to strike and scan to develop the image, the brightness of the image depends largely upon and increases with the velocity of the electrons as they strike this screen. For this reason, the velocity 1 of the electrons has been increased to a value where a reasonably bright image is obtained on the fluorescent screen. The value or point to which the velocity of the electrons can be increased has had its limitations, in systems pro- 5 posed heretofore, for the reason that, as the velocity increases, the electrons lose their sensitivity to the. deflecting field proportionally. In other words, increase in the velocity increases the difficulty of deflection. If this is compensated by increasing the strength of the deflecting field a point is soon reached where the extremely high current for this purpose is prohibitive.

Another disadvantage resulting from the high velocity electrons, in constructions of cathode ray tubes proposed heretofore, has been found to be that, under such conditions, an undesirably high voltage is required on the grid for controlling the cathode ray. It appears that this voltage is, of necessity in these prior constructions, sufflciently high to develop=a very strong ionic activity in the region at the hot-oxide-coated filament or cathode, so that the ions are caused to bombard the filament violently enough to break down and destroy, in part at least, the oxide coating, or at any rate, to decrease appreciably the possible, normal life .of the filament cathode, the useful life of which depends upon maintenance of the oxide, cathode-emitting coating thereon.

With the foregoing in mind, it is one of the objects of the present invention to provide an improved system, of the character referred to, wherein the velocity of the electrons can be increased to any desirable value, to produce a very bright image on the fluorescent screen, without sacrificing sensitivity of the electrons to the defleeting field therefor, or making necessary undesirable increase in the strength of this field, and wherein the required control-voltage on the grid is at a conveniently low value and such as to guard against the decrease in the life of the cathode referred to.

Other objects and appear.

In accordance with my invention, the electrons advantages will hereinafter are emitted at a relatively low velocity from the electron gun of the cathode ray tube and, while at this low velocity, at which they are highly sensitive to a relatively weak deflecting field and can also be controlled by a relatively low voltage on the grid, are subjected to this field and controlled by the relatively low grid voltage, after which the velocity of the electrons is stepped up or increased to a very high point so that the electrons strike the fluorescent screen at extremely high velocity to cause a very bright image to be developed.

My invention resides in an improved method and apparatus of the character hereinafter describedand claimed.

For the purpose of illustrating my invention, an embodiment thereof is shown in the drawing, in which Fig. 1 is a diagrammatic view of a television system embodying the present improvements;

Fig. 2 is an enlarged detail fragmentary view, taken from Fig. 1;

Fig. 3 is a development of the section taken on line 3-3, Fig. 1; and Figs. 4 and 5 are fragmentary sectional views, showing modifications.

The cathode ray tube, designated generally by the reference numeral 10, is provided at one end thereof with the means or so-called electron gun, designated generally by the reference numeral 11, for developing a cathode ray 12 and directing the same to the other end 13 of the tube having fluorescent material 14 on the inner surface thereof providing a fluorescent screen.

A coating 14a, of silver or any other suitable electrically conductive material, is applied to the tube in any suitable manner, as in the construction disclosed in my co-pending application Serial No. 407,652, filed November 16, 1929, and assigned to the Westinghouse Electric and Manufacturing Company. The silver coating 14a is disposed between the end wall 13 and the fluorescent coating 14, and is sufficiently thin to be translucent, or practically transparent to light.

The electron gun is indicated as being of the general type disclosed in my co-pending appli-- cation referred to above, and includes a heater 15, a cathode 16, a grid 17 and an anode 18.

The receiving circuit may be of any suitable type to meet particular operating requirements. The circuit shown is of the general type disclosed in my co-pending application Serial No. 105 376,117, filed July 5, 1929, and assigned to the Westinghouse Electric 8: Manufacturing Company.

The transmitted energy is received by the antenna 19 to which is connected a tuning condenser 20, an inductor 21 and a ground connection 22. This circuit is coupled to a radiofrequency amplifier 23, of any suitable type,

which amplifier is followed by a detector and audio-frequency amplifier 24. The output of the audio amplifier is impressed upon a filter 25 which passes the framing-frequency only. A second filter 26 passes the scanning-frequency, while the picture impulses are impressed upon the primary winding of a transformer 27. The filter 25 supplies the circuit shown and to which are connected the deflecting coils 28 which develop an'electromagnetic field effective to cause vertical deflection of the ray 12.

The filter 26 supplies the circuit shown and to which are connected the coils 29 effective to develop an electromagnetic field for causing horizontal deflection of the ray 12.

The joint effect of the fields developed by the coils 28 and 29 causes the ray 12 to scan the fluorescent end 13-14 of the tube 10.

It is proposed to make the adjustments such as to impress upon the anode 18, from the battery or other source 30, a positive potential of 500 volts.

A cup-shaped structure 31, made of fine wire mesh, is disposed in the tube 10, as shown, with its open end extending inwardly toward the electron gun 11. The structure 31 has a snug fit in the interior of the tube, and the left-hand end portion is in contacting relation with the silver coating 32 over the interior surface of the tube between the lines 33 and 34.

The bottom 35 of the structure 31 constitutes a screen through which the electrons of the ray 12 pass to the fluorescent screen 13-14, as indicated by the arrows 36 in Fig. 2;

It is proposed to impress upon the silver coat-v ing 32 and the screen 35, electrically connected thereto, a positive potential, from the battery or other suitable source 37a, of 2,000 volts.

The tube 10 is provided at the extreme righthand end thereof with a relatively thick interior coating of silver in the form of a ring 37 which overlaps the adjacent edge portion of the thin silver coating 14a, as indicated in Fig. 3, to make electrical connection between the latter, through a connection 38, with a battery or other source 39 serving to impress on the fluorescent anode 13-14 a positive potential of about 20,000 volts.

The operation is as follows: The resultant force developed by the coils 28 and 29 operates to deflect the ray 12 as the electrons are emitted from the gun 11 at the relatively low velocity, as determined by the positive potential on the first accelerating anode 18. At this relatively low velocity, the electrons are highly sensitive to the field developed by the deflecting coils 28 and 29, and follow the same exactly. The electrons, as they leave the oxide-coated surface of the cathode 16 at this relatively low velocity, are also subject to exact control by the relatively low voltage on the grid 17.

Immediately after the electrons pass beyond the influence of the coils 28 and 29, their velocity is increased materially under the influence of the high positive potential of 2,000 volts on the second accelerating anode or screen 35. When the electrons reach the screen 35, therefore, they are travelling at a very high velocity, and most of them pass through the openings in the screen, as indicated by the arrows 36, and strike the fluorescent coating 14, causing a bright spot to appear over the region 40 observed When the electrons strike from the exterior of the tube. .The electrons are focused to a small spot on the screen 35 under the influence of the high positive potential on the second anode 32. The electrons of the ray which strike the wire of the mesh screen 35 also initiate a secondary emission from this screen to the fluorescent coating 14, as indicated by the arrows 41. This secondary emission also strikes the coating 14 to increase the brightness of the spot indicated by reference numeral 40.

By reason of the relatively large potential difference between the second anode 35 and the third anode 13-14, the latter being positive with respect to the former, the velocity of the electrons is stepped up further to an extremely high value or point during that part of their movement from the anode or screen 35 to the anode 13-14. the fluorescent coating 14, therefore, theyare travelling at an extremely high velocity, and accordingly cause a very bright spot to appear over the spot or region 14 as viewed from the exterior of the tube. This brightness, as stated above, is further increased by utilization of the secondary. electron emission from the screen 35 to the coating 14, as indicated by the arrows 41.

The electrons, as the same strike any of the individual spots on the fluorescent coating 14, are conducted back to the cathode 16 by way of the silver coatings 14a and 37 and connection 38. The electrons are thus prevented from accumulating at any spot on the fluorescent coating.

The image developed on the end wall structure 13-14 of the tube 10 may be projected through a suitable lens or lens system 42 onto a suitable screen 43 for observation.

In the modification illustrated by Fig. 4, a suitable window construction 44 is inserted in the right-hand end of the tube and takes the place of the fluorescent coating 14 shown in Figs. 1 and 2. This construction is sometimes referred to as a Wehnelt window, and is characterized by the fact that electrons, when travelling at a relatively highvelocity, are capable of passing through it.

The construction and manner of operation in' Fig. 4 is otherwise the same as in Figs. 1 and 2. The electrons passing throuh the Wehnelt window, as indicated by the arrow 45, may be made to fall upon a photographic plate or film 46, on which the received image is recorded.

The voltages impressed upon the three anodes 18, 35 and 13-14 may be varied over a wide range to suit diiferent requirements. In this connection, it is contemplated in some cases to impress upon the first anode 18 a positive potential of 500 volts, to impress upon the second anode 35 a positive potential of 3,000 volts, and to impress upon the third anode 13-14 a positive potential of 60,000 volts. The potential on the third anode 13-14 is, therefore, twenty times greater than that on the second anode 35. is seen that difficulties might arise in the way of providing adequate insulation between the anodes 13-14 and 35 to withstand the high potential difference between the same. In cases where this difiiculty might arise, it is proposed to increase the distance between these anodes by such amount as would be required. For this purpose, the length of the tube 10 is increased, as shown in Fig. 5, and a suitable focusing coil 47 disposed about the tube between the second and third anodes 35 and 13-14 to develop an electromagnetic field effective to so focus the electrons that they travel in substan tially parallel paths, without distortion, from the second anode or screen 35 to the third anode or fllwrescent screen 13-14. A suitable water jack- Under such conditions, it 13:

et ,48, having inlet and outlet connections 49 and 50, respectively, may be built as shown around the third anode 13-14 where this is found to be advantageous for the purpose of removing heat developed incident to normal operation of the tube.

. same as that illustrated by Figs. 1 and 2.

From the foregoing it will be seen that in my improved method for communication by television, the deflecting force or forces are developed and applied to the electrons as they are emitted from the electron gun at a relatively low velocity whereat the same are highly sensitive and responsive to the deflecting fields, after which the velocity of the electrons is increased in steps to an extremely high velocity at which the electrons strike the fluorescent screen or third anode 13-14 and, assisted by the secondary emission, indicated in Fig. 2 by the arrows 41, cause a very bright spot to appear over the spot or region 40 for observation from the exterior of the tube. While but one anode has been shown interposed between the first anode 18 and the endmost anode 13-14, it is contemplated to employ, in some cases, a plurality of interposed anodes, consecutively disposed in the tube, the positive potential on each anode increasing in value over that of the next adjacent anode nearer to the gun 11, so that the velocity of the electrons is increased in a relatively large number of steps, the number of steps being equal to the number of anodes and the highest positive potential and the greatest velocity of the electrons being at the endmost or last anode 13-14.

From the foregoing it will be seen that my invention provides for an increase in the velocity of the electrons to a value or point far above that which has been practical in television systems pro" posed heretofore and that, even with this extremely high velocity of electrons, only a relatively weak deflecting field is required to cause the cathode ray to properly scan the fluorescent screen, and a relatively low grid voltage is required to control the ray.

Although I have shown and described a specific embodiment of my invention, it is understood that the same is susceptible to many modifications, such as in the size, shape and arrangement of the parts, without departing from the spirit of my invention or the scope of the appended claims.

I claim as my invention:

1. In a cathode ray device of the character described for reproducing a picture, means for producing a ray of electrons of relatively low velocity, means for deflecting the low-velocity ray, means for controlling the intensity of the low-velocity ray in accordance with received picture signals, means for accelerating the ray of electrons after deflection and intensity-control thereof, electrode structure scanned by the ray and bombarded during the scanning action by the electrons'comprising the ray to produce secondary electron emission from said electrode structure at a velocity relatively high with respect to the initial ray velocity, and a fluorescent screen disposed in close proximity to said electrode structure and more sensitive to high velocity electrons than to low velocity electrons for bombardment by the electrons of secondary emission to reproduce the picture.

2. A television receiving device of the cathode ray type comprising an evacuated container, an electron source within said container, an electrically conductive target element supported from a wall of said tube opposite said electron source, a connection from said target element to the exterior of said container, a plurality of axially consecutive substantially concentric anode structures within said container, one of said anode structures lioiiuv, ('lllll|lll.tl\ ll\' (illilli'lfllll to an electron-permeable partition disposed adjacent said target element, and connections extending from said anode structures to the exterior 01' said. container, whereby electrons from said source may be subjected to a stepped potential gradient between said source uiulv will target clclnohl; and may be caused to impinge upon said electron permeable partition at silllicl iil-ly high velocity to give rise to secondary emission and the secondary electrons he :icreleraizeil toward said target element.

3. The invention set forth in claim 2 characterized in that the target element is electron-permeable.

4. The invention set forth in claim 2 characterized in that the interior surface of the target element is overlain by a coating of fluorescent material.

5. The invention set forth in claim 2 characterized in that the electron-permeable partition is constituted by a reticulated metallic screen.

6. The invention forth in claim 2 characterized in that the targetelement is constituted by a conductive coating on the inner surface of the end wall of the container and additionally characterized in that the said element is overlain by a coating of fiourescent material.

7. A television receiving device of the cathode ray type comprising an evacuated container wherein is mounted an electron-source, a conductive coating on an inner wall of said container opposite said source, plurality of coaxial anode structures supported within said container between said source and said coating, one of said structures terminating in a reticulated screen adjacent and substantially parallel to the conductive coating, and fluorescent material on said coating, whereby electrons from said source may be caused to impinge upon the reticulated screen at sufficiently high velocity to give rise to secondary emission and the secondary electrons be accelerated toward said conductive coating.

8. The method of operating a television device which comprises causing the emission of an electron stream, deflecting said stream for scanning purposes, accelerating the stream after deflection thereof, bombarding an electron-translucent screen with said stream to cause secondary emission and accelerating the secondary electrons to reproduce an image through impact upon a fluorescent screen.

9. The method of operating a television receiving device of the cathode ray type having an electron source, a fluorescent screen, and a reticulated screen disposed closely adjacent to and substantially parallel with said fluorescent screen, which comprises causing primary electrons to be emitted from said source, subjecting said primary electrons to a stepped potential gradient from said source toward said reticulated screen, causing the primary electrons to strike the reticulated screen with sufficient velocity to give rise to secondary electrons and causing said primary and said secondary electrons to be accelerated toward said fluorescent screen.

VLADIMIR KOSMAN ZWORYKIN. 

